Defining Predation (+,-)




  • An organisms that consumes all or part of another organism (prey)
    • benefits its own fitness
    • reduces the growth, fecundity and survival of the prey population


1. True predators: attack, kill & consume

2. Grazers: attack many things, eat only a part and do not kill

3. Parasites: infect one host, keep alive in short term

Parasitoid Bodysnatchers: complicating predator definitions…



Predator behavior



  • Behaviors to capture prey differ vastly
    • consumption rate:
    • consumption rate impacts populations


  • True predators and grazers are mostly foragers
    • searching (active)
    • sit and wait (passive)


  • Prey behavior (evasiveness) impacts consumption rate


  • Parasite rely on transmission
    • direct contact is density dependent

Optimal Foraging Theory






  • Obtaining food provides energy


  • Searching for and capturing food requires energy


  • Foraging is a banking problem: Return on Investment


  • To maximize fitness a predator must balance these
    • alpine bumble bees

Optimal foraging should be related to density

Optimal foraging in African predators: Energy use




  • Calorie use by big predators
    • Cheetahs = 9,000 Kj
    • Wild dogs = 15,000 Kj
    • Lions = ?
    • Humans = 9000 Kj


  • Foraging Strategies
    • Laziness
    • Thievery
    • Group hunting
    • Seasonal prey choice

Optimal foraging in African predators: Energy use


Optimal foraging in African predators: Energy use


Consumption is an agent of natural selection: Defense


Predators also adapt to prey (Cattau et al. 2017)


Predation may promote biodiversity





  • If they consume the strongest competitor
    • invasive species…


  • Relieves competitive pressure on other species enabling coexistence


  • Predation structures communities

Predator vs Prey populations (Basics)


Impacts of predation on populations is complex…




  • Behavior/adaptations of predators and prey
    • natural selection


  • Compensatory responses


  • Life histories


  • Start Simple: Lynx vs Rabbit

Lotka Voltera: Modelling predator-prey dynamics



  1. Start with a lot of rabbits, who does well?
  2. Populations of lynx will ….
  3. Why does time matter at this step?
  4. Populations of prey will….
  5. Food for predators will
  6. Over time predator populations will ….


  • These predator-prey patterns are described in the Lotka-Voltera 2 species model
    • 2 basic components:
    • P = # of predators
    • N = # of prey

Lotka-Voltera predicts coupled population cycles


Lotka Voltera



  • With no predators, prey populations (N) increase exponentially
    • dN/dt = rN
    • r = growth rate


  • Predators remove prey at some rate
    • dN/dt = rN - aPN
    • a = attacking efficiency



  • Prey stable when dN/dt = 0
  • In the absence of food, predator populations (P) will decline
    • dP/dt = -qP
    • q = mortality rate


  • Mortality buffered by births (faPN)
    • dP/dt = faPN -qP
    • food gain (aPN)
    • efficiency of food to offspring (f)


  • Predator stable when dP/dt = 0

Start each population cycle at the zero isocline


Leftover questions: Are predator-prey cycles that simple?












  • Leftover questions: Are the cycles sustainable?